Comparison of intravenous lipid emulsion, bicarbonate, and tailored liposomes in rabbit clomipramine toxicity

Lipid Emulsion to Treat Acute Poisonings: Mechanisms of Action, Indications, and Controversies

Biodetoxification using intravenous lipid emulsion (ILE) in acute poisoning is of growing interest. As well as for local anesthetics, ILE is currently used to reverse toxicity caused by a broad-spectrum of lipophilic drugs. Both pharmacokinetic and pharmacodynamic mechanisms have been postulated to explain its possible benefits, mainly combining a scavenging effect called "lipid sink" and cardiotonic activity. Additional mechanisms based on ILE-attributed vasoactive and cytoprotective properties are still under investigation. Here, we present a narrative review on lipid resuscitation, focusing on the recent literature with advances in understanding ILE-attributed mechanisms of action and evaluating the evidence supporting ILE administration that enabled the international recommendations. Many practical aspects are still controversial, including the optimal dose, the optimal administration timing, and the optimal duration of infusion for clinical efficacy, as well as the threshold dose for adverse effects. Present evidence supports the use of ILE as first-line therapy to reverse local anesthetic-related systemic toxicity and as adjunct therapy in lipophilic non-local anesthetic drug overdoses refractory to well-established antidotes and supportive care. However, the level of evidence is low to very low, as for most other commonly used antidotes. Our review presents the internationally accepted recommendations according to the clinical poisoning scenario and provides the precautions of use to optimize the expected efficacy of ILE and limit the inconveniences of its futile administration. Based on their absorptive properties, the next generation of scavenging agents is additionally presented. Although emerging research shows great potential, several challenges need to be overcome before parenteral detoxifying agents could be considered as an established treatment for severe poisonings.

Heterogeneity and bias in animal models of lipid emulsion therapy: a systematic review and meta-analysis

INTRODUCTION

Clinicians utilize lipid emulsion to treat local anesthetic toxicity and non-local anesthetic toxicities, a practice supported by animal experimentation and clinical experience. Prior meta-analysis confirmed a mortality benefit of lipid emulsion in animal models of local anesthetic toxicity but the benefit of lipid emulsion in models of non-local anesthetic toxicity remains unanswered. Further, swine suffer an anaphylactoid reaction from lipid emulsions calling into question their role as a model system to study lipid, so we examined swine and non-swine dependent outcomes in models of intravenous lipid emulsion.

METHODS

We conducted a systematic review and meta-analysis examining the use of lipid emulsion therapy in animal models of cardiac toxicity. We quantified mortality using a random-effects odds-ratio method. Secondary outcomes included survival in the following subgroups: local-anesthetic systemic toxicity, non-local anesthetic toxicity, swine-based models, and non-swine models (e.g., rat, rabbit and dog). We assessed for heterogeneity with Cochran's Q and I². We examined bias with Egger's test & funnel plot analysis.

RESULTS

Of 2784 references screened, 58 met criteria for inclusion. Treatment with lipid emulsion reduced chance of death in all models of toxicity with an odds ratio of death of 0.26 (95% CI 0.16-0.44, Z-5.21, p < 0.00001, Cohen's-d = 0.72, n = 60). Secondary outcomes confirmed a reduced chance of death in models of local anesthetic toxicity (OR 0.16 {95% CI 0.1-0.33}) and non-local anesthetic toxicity (OR 0.43 {95% CI 0.22-0.83}). Heterogeneity (Cochran's Q 132 {df = 59, p < 0.01}, I ² = 0.55) arose primarily from animal-model and disappeared (I ² < = 0.12) when we analyzed swine and non-swine subgroups independently. Swine only benefited in models of local anesthetic toxicity (OR 0.28 {95% CI 0.11-0.7}, p = 0.0033) whereas non-swine models experienced a homogeneous benefit across all toxins (OR 0.1 {95% CI 0.06-0.16}, p < 0.00001). Egger's test identified risk of bias with outliers on funnel plot analysis.

DISCUSSION

Lipid emulsion therapy reduces mortality in animal models of toxicity. Heterogeneity arises from the animal-model used. Swine only benefit in models of local anesthetic toxicity, potentially due to lipid dose, experimental design or swine's anaphylactoid reaction to lipid. Outlier analysis reinforced the need for appropriate dosing of lipid emulsion along with airway management and chest compressions in the setting of cardiac arrest.

Lipid emulsion in local anesthetic toxicity

PURPOSE OF REVIEW

Enthusiasm for regional anesthesia has been driven by multimodal benefits to patient outcomes. Despite widespread awareness and improved techniques (including the increasing use of ultrasound guidance for block placement), intravascular sequestration and the attendant risk of local anesthetic systemic toxicity (LAST) remains. Intravenous lipid emulsion (ILE) for the treatment of LAST has been endorsed by anesthetic regulatory societies on the basis of animal study and human case report data. The accumulated mass of reporting now permits objective interrogation of published literature.

RECENT FINDINGS

Although incompletely elucidated the mechanism of action for ILE in LAST seemingly involves beneficial effects on initial drug distribution (i.e., pharmacokinetic effects) and positive cardiotonic and vasoactive effects (i.e., pharmacokinetic effects) acting in concert. Recent systematic review by collaborating international toxicologic societies have provided reserved endorsement for ILE in bupivacaine-induced toxicity, weak support for ILE use in toxicity from other local anesthetics, and largely neutral recommendation for all other drug poisonings. Work since publication of these recommendations has concluded that there is a positive effect on survival for ILE when animal models of LAST are meta-analyzed and evidence of a positive pharmacokinetic effect for lipid in human models of LAST.

SUMMARY

Lipid emulsion remains first-line therapy (in conjunction with standard resuscitative measures) in LAST. Increasing conjecture as to the clinical efficacy of ILE in LAST, however, calls for high-quality human data to refine clinical recommendations.

Parenteral emulsions and liposomes to treat drug overdose

Drug overdoses from both pharmaceutical and recreational drugs are a major public health concern. Although some overdoses may be treated with specific antidotes, the most common treatment involves providing supportive care to allow the body to metabolize and excrete the toxicant. In many cases, supportive care is limiting, ineffective, and expensive. There is a clear medical need to improve the effectiveness of detoxification, in particular by developing more specific therapies or antidotes for these overdoses. Intravenous lipid emulsions (ILEs) have been investigated as a potential treatment for overdoses of local anesthetics and other hydrophobic drugs. While ILE therapy has been successful in several cases, its use beyond local anesthetic systemic toxicity is controversial and its mechanism of detoxification remains a subject of debate. ILEs were not originally developed to treat overdose, but clarifying the mechanisms of detoxification observed with ILE may allow us to design more effective future treatments. Liposomes are highly biocompatible and versatile formulations, thus it was a natural step to explore their use for drug overdose therapy as well. Several researchers have designed liposomes using a variety of approaches including surface charge, pH gradients, and inclusion of enzymes in the liposome core to optimize the formulations for detoxification of a specific drug or toxicant. The in vitro results for drug sequestration by liposomes are very promising and animal trials have in some cases shown comparable performance to ILE at reduced lipid dosing. This narrative review summarizes the current status and advances in the use of emulsions and liposomes for detoxification and also suggests several areas in which studies are needed for developing future therapies.

Cardiac depression induced by cocaine or cocaethylene is alleviated by lipid emulsion more effectively than by sulfobutylether-β-cyclodextrin

OBJECTIVES

Cocaine intoxication leads to over 500,000 emergency department visits annually in the United States and ethanol cointoxication occurs in 34% of those cases. Cardiotoxicity is an ominous complication of cocaine and cocaethylene overdose for which no specific antidote exists. Because infusion of lipid emulsion (Intralipid) can treat lipophilic local anesthetic toxicity and cocaine is an amphipathic local anesthetic, the authors tested whether lipid emulsion could attenuate cocaine cardiotoxicity in vivo. The effects of lipid emulsion were compared with the metabolically inert sulfobutylether-β-cyclodextrin (SBE-β-CD; Captisol) in an isolated heart model of cocaine and cocaethylene toxicity to determine if capture alone could exert similar benefit as lipid emulsion, which exhibits multimodal effects. The authors then tested if cocaine and cocaethylene, like bupivacaine, inhibit lipid-based metabolism in isolated cardiac mitochondria.

METHODS

For whole animal experiments, Sprague-Dawley rats were anesthetized, instrumented, and pretreated with lipid emulsion followed by a continuous infusion of cocaine to assess time of onset of cocaine toxicity. For ex vivo experiments, rat hearts were placed onto a nonrecirculating Langendorff system perfused with Krebs-Henseleit solution. Heart rate, left ventricle maximum developed pressure (LVdevP), left ventricle diastolic pressure, maximum rate of contraction (+dP/dtmax), maximum rate of relaxation (-dP/dtmax), rate-pressure product (RPP = heart rate × LVdevP), and line pressure were monitored continuously during the experiment. A dose response to cocaine (10, 30, 50, and 100 μmol/L) and cocaethylene (10, 30, and 50 μmol/L) was generated in the absence or presence of either 0.25% lipid emulsion or SBE-β-CD. Substrate-specific rates of oxygen consumption were measured in interfibrillar cardiac mitochondria in the presence of cocaine, cocaethylene, ecgonine, and benzoylecgonine.

RESULTS

Treatment with lipid emulsion delayed onset of hypotension (140 seconds vs. 279 seconds; p = 0.008) and asystole (369 seconds vs. 607 seconds; p = 0.02) in whole animals. Cocaine and cocaethylene induced dose-dependent decreases in RPP, +dP/dtmax, and -dP/dtmaxabs (p < 0.0001) in Langendorff hearts; line pressure was increased by cocaine and cocaethylene infusion, but not altered by treatment. Lipid emulsion attenuated cocaine- and cocaethylene-induced cardiac depression. SBE-β-CD alone evoked a mild cardiodepressant effect (p < 0.0001) but attenuated further cocaine- and cocaethylene-induced decrements in cardiac contractility at high concentrations of drug (100 μmol/L; p < 0.001). Finally, both cocaine and cocaethylene, but not ecgonine and benzoylecgonine, inhibited lipid-dependent mitochondrial respiration by blocking carnitine exchange (p < 0.05).

CONCLUSIONS

A commercially available lipid emulsion was able to delay progression of cocaine cardiac toxicity in vivo. Further, it improved acute cocaine- and cocaethylene-induced cardiac toxicity in rat isolated heart while SBE-β-CD was effective only at the highest cocaine concentration. Further, both cocaine and cocaethylene inhibited lipid-dependent mitochondrial respiration. Collectively, this suggests that scavenging-independent effects of lipid emulsion may contribute to reversal of acute cocaine and cocaethylene cardiotoxicity, and the beneficial effects may involve mitochondrial lipid processing.

Multi-modal contributions to detoxification of acute pharmacotoxicity by a triglyceride micro-emulsion

Triglyceride micro-emulsions such as Intralipid® have been used to reverse cardiac toxicity induced by a number of drugs but reservations about their broad-spectrum applicability remain because of the poorly understood mechanism of action. Herein we report an integrated mechanism of reversal of bupivacaine toxicity that includes both transient drug scavenging and a cardiotonic effect that couple to accelerate movement of the toxin away from sites of toxicity. We thus propose a multi-modal therapeutic paradigm for colloidal bio-detoxification whereby a micro-emulsion both improves cardiac output and rapidly ferries the drug away from organs subject to toxicity. In vivo and in silico models of toxicity were combined to test the contribution of individual mechanisms and reveal the multi-modal role played by the cardiotonic and scavenging actions of the triglyceride suspension. These results suggest a method to predict which drug toxicities are most amenable to treatment and inform the design of next-generation therapeutics for drug overdose.